Fix syntax

Author: antonio-rojas

src/sage/features/threejs.py

@@ -26,9 +26,7 @@ def __init__(self):
         """
         from sage.env import sage_data_paths, THREEJS_DIR
 
-        threejs_search_path = THREEJS_DIR or list(sage_data_paths('jupyter/nbextensions/threejs-sage')) +
-            sage_data_paths('threejs-sage') +
-            sage_data_paths('threejs')
+        threejs_search_path = THREEJS_DIR or list(sage_data_paths('jupyter/nbextensions/threejs-sage')) + list(sage_data_paths('threejs-sage')) + list(sage_data_paths('threejs'))
 
         try:
             version = self.required_version()